Electricity posts & distribution voltages, etc.

[David Paste]

Hello,

'They' are installing a new power line near here using this type of pole:

sort of voltage / current would this kind of pole supply?

There are also some of these nearby:

question!

In a recent thread about power cables to houses in the sticks, someone mentioned that the electricity companies aren't too keen on installing (I think it was...) 3,000 volt wires on poles, instead preferring a higher voltage. Why is this? Are the transformers-in-a-can that strap to the utility poles of a similar price to the lower priced ones? I only make that supposition as it would seem more sensible to supply at a higher voltage as close as possible to the customer's premises to reduce the losses. Is this in any way right?!

Thanks in advance,

David Paste.

[Nick]

In message , David Paste writes

They're about to install one near me. An existing pole has a planning application notice on it with details, including the voltage, so it may be worth looking nearby if no-one here is able to be precise.

[Nightjar]

> What sort of voltage / current would this kind of pole supply?

> Same question!

The second photo looks like an 11kV line feeding a pole mounted transformer. I've not seen the first type, but the insulators are obviously for a higher voltage, perhaps 33kV, which would be the next step up in the distribution system.

Colin Bignell

[Andy Burns]

> I've not seen the first type, but the insulators are

The 33kV ones I notice are mostly double-post ones, like this

the type in David's photo could well be a new 33kV variation

[Andrew Gabriel]

Only place I've seen those in the UK is on the A505 heading towards Cambridge:

don't know the voltage.

As others said, that's 11kV.

11kV is the lowest. 33kV is the next size up.

On cost/voltage drop basis, rough rule of thumb is 1kV per mile of cable run, so an 11kV cable will do 10 miles, whereas a 33kV run will do

30 miles. But the load is important too, and you may well find a 33kV cable on a shorter run if the load is high enough to merit it.

[Dave Liquorice]

I would say that 3 = 33kV would hardly ever be right. Round here the majority of the distribution is 3 phase (thus wires) @ 11k. There are a number of two wire spurs but the main distribution is all 3 phase.

The local substation is fed with 33kV and it looks very similar to the 11kV but the insulators are just a little bigger, IIRC they are two stacked saucers with a skirt rather than just the one for 11kV.

[Dave Liquorice]

Doesn't work like that. Provided the current in all phases is the same there is no neutral current so you don't need a neutral wire. A fair amount of care is taken to ensure that the phases are (more or less) in balance.

Where there is a neutral it is bonded to ground (as in the big round thing we inhabit) at the sub station. The grid does have a neutral wire, that's the much smaller wire running pylon top to pylon top.